An axial flow fan may be used to produce a flow of cooling air through the heat exchanger components of a vehicle. For example, an airflow generator used in an automotive cooling application may include an axial flow fan for moving cooling air through a liquid-to-air heat exchanger such as an engine radiator, condenser, intercooler, or combination thereof. The required flow rate of air through the fan and change in pressure across the fan vary depending upon the particular cooling application.
Generally, axial flow fans are designed by using a free vortex or forced vortex flow/pressure distribution. A free vortex design ensures that a constant total pressure rise is achieved everywhere across the span of the fan blade. The forced vortex designs are usually a slight deviation from the free vortex designs since the forced vortex designs maintain a relatively two-dimensional flow through the blade passage.
Conventional fans are often designed such that the blade profiles work close to their peak ratio of lift to drag. The efficiency of the fan is related to how closely the blades operate to their peak lift to drag value. The high lift coefficient on the blades results in a strong pressure pulse. Gutin's principle shows that strong pressure pulse results in a tonal component of noise at the blade passing frequency.
Accordingly, there is a need to provide a fan to reduce the tonal component while maintaining the flow and pressure generated by the fan.